Q. Who contributes more to the USA’s recent “immigrant-stock”, legals or illegals?A.It’s about 50-50. Half the USA’s immigrant-stock is of “illegal background”, by my calculation. (Either originally illegal but now legal, of illegal parentage, or presently illegal).

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Below is how the “about half” figure was derived:
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Given: There are 12 million illegal immigrants in the USA. (Some say more, I will be conservative and assume it is only 12).
Unknown: The total number of “purely legal” immigrants.
Unknown: The total number of children born in the USA to legal immigrants.
Unknown: The total number “legalized illegals”, i.e. legals who were originally illegal”.
Unknown: The total number of children born in the USA to illegal immigrants.

Using government statistics, we can find answers to these unknowns.
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1.) Family-Based Visas: U.S. citizens, and in some cases foreign permanent-residents, can bring-in immediate family members. (This has been dubbed “Chain-Migration”).
2.) All Non-Family Legal Avenues: Employment visas, Refugees, The Diversity Lottery, and other miscellaneous non-family visas).
3.) Legalized Illegals: For simplicity’s sake [See Note-#4], this includes three subcategories: 1.) Those illegals who were legalized by Reagan; 2.) The children born to illegals on U.S. soil, all of whom are automatically given U.S. citizenship; 3.) The illegal-immigrant parents who gain legality by virtue of having a U.S. citizen child (“anchor baby”).

To restate the original “unknowns”: What share of foreigners who have been given permanent-residency by the USA in the past generation fall into category-#3?

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For an answer we can look at INS/USCIS data (and a bit of CDC data on births, as well as the old standby the Census Bureau).

From 1986-2009, we find:

“Purely Legal” Immigrants
— 18.44 million foreigners were given permanent residency status [768,00/year] with no “first-hand” connection to illegal-immigration. (Categories #1 and #2 above). [See Note-#1].
— 11.22 million babies were born to legal immigrants in the USA, 1986-2009. This is 11.7% of total births in that period. [See Note-#3].
[TOTAL: 29.66 million, “purely legal” immigrant stock, 1986-2009]

Illegals, Legalized
— 2.69 million illegal immigrants were amnestied by Reagan.
— 8.13 million babies were born to illegals on U.S. soil ’86-’09, and automatically given U.S. citizenship under the prevailing interpretation of the 14th-Amendment. [See Note-#3].
— 2.62 million Illegal immigrant parents were given permanent status 1986-2009 because they had a U.S.-citizen child (“anchor baby”). [See Note-#4].
— [TOTAL: 13.44 million: “Illegal-Immigrant-Stock Made Legal” 1986-2009 (560,000/year)]
________________________________________________________Summary of Background of Legal Immigrants:
— 43.1 million foreign-origin persons were given permanent-residency by the USA either by act of government or by being born there, 1986-2009.
— 31.2% of these legals are of “illegal immigrant stock”.

True Share of “Legalized Illegals” Up to 35%
31% is an undercount of the illegal-share. Once an illegal is legalized, any children they would have would be counted as births to legal-immigrants. Strictly-speaking, such babies are of “illegal stock” (i.e., the reason they are in the USA is someone entered illegally). For example, of the millions of illegals legalized by Reagan, any children they would have had post-legalization would be counted under “purely legal” here. Accounting for this, the true figure of “illegal stock” among USA’s recent immigrant stock must be ticked up a couple points, perhaps reaching 35%.

True Illegal Immigrants
The terminology involved here can be confusing, but take note especially that actual “illegal immigrants” (undocumented immigrants of no recognized legal status in the USA) have not been discussed here at all. The numbers above are only what the U.S. federal government provides firm data for.
The most common estimate for actual illegal immigrants is 12 million.

Note #2: These figures include both new arrivals and those foreigners in the USA receiving “adjustment of status” to permanent-residency.

Note #3: For “anchor baby” births: Records show that roughly 42% of immigrant births in the USA are to the fecund illegal immigrants. Overall immigrant (legal+illegal) birth share is as follows — 1980: 9%, 1990: 15%, 2002: 23%, [2009: 27%, extrapolated]. Using birth data from the CDC and population data from the U.S. Census (2000s, 1990s), we find that 8.4% of births overall during the period were to illegal immigrants and 11.7% were to legal immigrants. There were 96.24 million recorded births in the USA from 1986 to 2009.

Note #4: Not all of those listed under DHS’ “parents of citizens” category for those given permanent-residency are connected to anchor-babies. Presumably the vast majority are. The total number is used here. The overcount is likely approximately offset by those illegals who have been defacto legalized under miscellaneous programs that have not been counted here, e.g. the Nicaragua Adjustment and Central American Relief Act (NACARA), which has legalized 70,000 illegals.

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Comments on potential weaknesses in the methodology used here, and how to improve them, are welcome. The point is to find the truth of this matter.